What is the ruling on a son continuing to benefit from a shop that his father verbally leased 20 years ago, and which he (the son) transformed into a bakery that prospered through his efforts, then after his father's death, the heirs claim ownership of the shop, and one of the heirs does not agree to the lease and demands his right?

What you mentioned about your father renting this shop to your brothers without a contract carries two possibilities:

1. The contract was not written down, yet the pillars and conditions of a lease were fulfilled: In this case, the lease is valid and does not terminate upon the death of one of the contracting parties. The heirs of the lessee take his place until the end of the specified term.

2. The rental period was not specified: In this case, the contract is void and must be rescinded. Then, a new contract should be drawn up in which the agreed-upon period is mentioned. As for the past period, it should be calculated based on the fair market rent, and the profits from the shop during that period are lawful for you.